Electrical power for operating a wide variety of electronic circuit-based products, such as portable and hand-held devices including notebook computers, personal digital assistants, cell phones, and the like, is typically supplied by one or more direct current (DC) power sources, including rechargeable, single-cell batteries. As one would expect, the ongoing demand for increased functionality and longer run time of these battery-powered products has led to the development of power conservation mechanisms, that either sense or are informed that the electronic device is not being actively used, and then take action to reduce power consumption.
As a non-limiting example, the power control circuitry of a laptop computer will customarily transition the computer's power supply from ‘active’ mode to ‘sleep’ or ‘quiescent’ mode of operation when the user closes the display lid or fails to manipulate an input/output device within some prescribed period time. During this idle mode, the power control circuitry functions to keep only essential portions of the operational capability of the computer active, in order to reduce the power drain. Subsequently, in response to the user reinitiating use of the device, the power conservation circuit switches back to the main supply.
To date, circuits that have employed for this purpose customarily contain some form of power supply coupling (transistor) circuit that controllably switches between the main supply and a reduced quiescent mode auxiliary source. A primary drawback to these circuits is the substantial switching transients that are generated when the coupling circuit transitions between the two supply paths. This noise is often due to the fact that the switching operations employ substantial ‘fully off’ and ‘fully on’ biasing of the transistors through which the power supply voltages are routed.